Radiation in the Environment radioactivity and radioactive decay biological impact and dose sources of radiation in the environment natural anthropogenic case study (Chernobyl)

Uranium-238 natural decay series. Po Pb Bi At Tl Rn Ra Th U Pa 206 210 214 218 222 226 230 234 238 81 84 83 82 85 86 88 90 92 91 (stable) Uranium-238 natural decay series.  

Radioactive Decay Laws: Why are some nuclei unstable? Activity (rate of decay) n p n = p n > p [Units: Becquerel (Bq) = 1 disintegration/s] N=Noe-t and t½ = 0.693/ Nuclear Instability multiple isotopes e.g. 235U and 238U

Some Types of Radioactive Emissions Radiation Symbol Description Charge Mass No.(amu) alpha  He nucleus +2 4 beta  nuclear electron -1 0 gamma  em radiation - - neutron n nuclear particle 0 1

Radiation and Living Organisms What does radiation do to the body? Ionising radiation ions and radicals abnormalities and cancers Cell damage: Crypt cells white blood cells cells which produce red and white blood cells At high doses Radiation sickness (syndrome) Symptoms: nausea, vomiting, diahorrea, fatigue

Radiological dose Absorbed dose: amount of energy absorbed by tissue Unit = Gray 1 Gy = transfer of 1J to 1 kg Dose equivalent: absorbed doses multiplied by a quality factor (QF) which reflects the damaging power of the radiation. DT (Sv) = DA (Gy) x QF QF for X-ray,  and  = 1 QF for  = 20 Effective dose dose equivalent weighted to account for the different equivalent: susceptibilities of various tissue types to radiation damage HE = TDTWT WT weighting factor (International Commission on Radiological Protection (ICRP))

ICRP Weighting Factors (WT) Tissue or organ WT testes or ovaries 0.25 breast 0.15 red bone marrow 0.12 lung 0.12 thyroid 0.03 bone surfaces 0.03 remainder 0.3 Whole body total 1.00 Maximum Permissable Dose (Whole Body) Damage to tissue depends on: dose received gender age HE (max) = 50(N-18)

External vs Internal exposure Absorbed dose  (distance)-1 (inverse square law) While for most of us, most radiation events may involve a small external dose, due to the distance between us and source, ingestion of radionuclides can provide us with a high dose from a dilute source at close range. Our physiological processes may also cause certain isotopes to concentrate in various body tissues: 90Sr, 89Sr, 32P bones 131I thyroid In addition to a nuclides radiological half-life it is necessary to define an analogous biological half-life, tbiol. This allows an effective half-life, teff, to predict the impact of radioisotope ingestion. Teff = (tbiol.trad)/[(tbiol+trad)]